1. Field of the Invention
One embodiment of the present invention relates to a semiconductor device and a device including the semiconductor device.
Note that in this specification, a semiconductor device means a general device that can function by utilizing semiconductor characteristics. An electrooptical device, a semiconductor circuit, and an electronic device can all include a semiconductor device.
2. Description of the Related Art
A technique in which a transistor is formed using a semiconductor has attracted attention. The transistor is used in a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). As materials of the semiconductor that can be used in the transistor, silicon-based semiconductor materials have been widely known, but oxide semiconductors have been attracting attention as alternative materials.
For example, a transistor including an amorphous oxide semiconductor layer containing indium (In), gallium (Ga), and zinc (Zn) is disclosed in Patent Document 1.
Techniques for improving carrier mobility by employing a stacked structure of an oxide semiconductor layer are disclosed in Patent Documents 2 and 3.
It is known that a transistor including an oxide semiconductor layer has an extremely small leakage current when the transistor is off. For example, a low-power-consumption CPU utilizing such a small leakage current characteristic of a transistor including an oxide semiconductor layer is disclosed (see Patent Document 4).